| Radio frequency identification(RFID)is an automatic identification technology based on wirless transimission,which has been widely adopted for various data collection applications such as warehouse and retail item management.Several frequency bands has been assigned to RFID applications,in which system at Ultra High Frequency(UHF)band got a popular use in the past due to the suitability for long-range application.RFID reader antenna is a key part of RFID system,so research of UHF RFID reader antenna has become hot in recent years.The traditional reader antenna has an symmetrical radiation pattern.But in some specific environment,such as identifying the goods on belt conveyor,the radiation energy of antenna should be concentrated on conveyor nearby,while small of energy is required far above it.It means that design of radiation pattern is unsymmetrical and the main beam has some degree down tilt and half power beam width.This paper focused on the design and research of UHF RFID reader antenna element and linear array.Pattern synthesis was introduced into design of shaped-beam antenna to realize radiation pattern that we proposed a 28odown-tlit and 22ohalf power beam width in the main beam previously.Totally this paper was divided into three parts,which included the design of UHF RFID reader antenna element,pattern synthesis of UHF RFID reader antenna linear array and design and fine-tunning of shaped-beam of UHF RFID reader antenna array.Firstly,the operating principle and analytical method were introduced into this paper including method of transmission line,theory of cavity mode,multiplication of radiation pattern,and array factor versus frequency.It was important to provide guidance for the last antenna design.Secondly,two UHF RFID reader antenna elements were proposed.One of them was linearly polarization in single band;another was circularly polarized in double band.Aperture-coupled patch configuration was adopted as array element in both of them.Thirdly,Methods of Dolph-Chebyshev and Woodward-Lawson with examples of MATLAB programming was introduced,in which the second method was used to fit the pre-defined radiation pattern.Furthermore,amplitude and phase of each corresponding antenna element were calculated,thus designing and simulating the power divider as feeding network of antenna linear array.Meanwhile,radiation pattern of shaped-beam antenna linear array and range of read of tag were measured and performance of pre-defined pattern was met well.At last,fine-tune in the main beam was realized by adding RF switch to change the path of transmission,which provided technical preparation for adding module of phase-shift to realize beam scanning furthermore. |
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